Dark state light recycling film and display

• US 7,301,592 B2
• Filed: 11/19/2004
• Issued: 11/27/2007
• Est. Priority Date: 11/19/2004
• Status: Active Grant

• Current Assignee: SKC Hi-Tech & Marketing Co., Ltd.
• Original Assignee: Rohm and Haas Denmark Finance A/S
• Inventors: Mi, Xiang-Dong
• Primary Examiner(s): Dudek; James A.
• Application Number:
  US10/992,923
• Publication Number:
  US 20060109398A1
• Time in Patent Office: 1,103 Days
• Field of Search: 349/98, 349/96
• US Class Current: 349/96
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A liquid crystal display has a backlight unit for providing substantially unpolarized illumination, a rear polarizer proximate the backlight unit for receiving the incident substantially unpolarized illumination and transmitting substantially polarized illumination. A liquid crystal spatial light modulator forms a modulated beam by selective, pixel-wise modulation of the polarization of the substantially polarized illumination. A color filter array transmits selected wavelengths of the modulated beam from the LC spatial light modulator. A front polarizer has a transmission axis for transmitting the portion of the modulated beam having polarization in alignment with the transmission axis. A reflective polarizing element is disposed between the liquid crystal spatial light modulator and the front polarizer for reflecting a portion of dark state light back toward the backlight unit.

Claims

1. A method of adjusting display brightness comprising operating a liquid crystal comprising in order

(a) a backlight unit for providing illumination;

(b) a rear absorptive polarizer disposed proximate the backlight unit for receiving the incident illumination and transmitting substantially polarized illumination;

(c) a liquid crystal spatial light modulator for forming a modulated beam by selective, pixel-wise modulation of the polarization of the substantially polarized illumination;

(d) an absorptive color filter array for transmitting selected wavelengths of the modulated beam from the LC spatial light modulator;

(e) a front absorptive polarizer having a transmission axis for transmitting the portion of the modulated beam having a polarization in alignment with the transmission axis; and

,

(f) a reflective polarizing element disposed between the liquid crystal spatial light modulator (c) and the front absorptive polarizer (e), the reflective polarizing element reflecting a portion of dark state light back toward the backlight unit,

wherein the backlight unit comprises at least one light source for which the light output can be controlled as a function of the number of dark pixels in the displayed image.

2. The method according to claim 1 wherein the light source is a light emitting diode and the brightness is controlled by the step of varying the drive current to a light emitting diode.